A TIME-OF-FLIGHT POWDER NEUTRON-DIFFRACTION STUDY OF TERNARY CHROMIUMSULFIDES, NIXCR3-XS4 (0-LESS-THAN-X-LESS-THAN-OR-EQUAL-TO-1.0)

Time-of-flight powder neutron diffraction has been used to investigate the distribution of nickel and chromium cations between two crystallo graphically independent sites in the series of ternary sulfides, NixCr 3-xS4 (0 less than or equal to x less than or equal to 1.0). These mat erials are isostructural with Cr3S4 (space group 12/m: a approximate t o 5.9 Angstrom, b approximate to 3.4 Angstrom, c approximate to 11.1 A ngstrom, beta approximate to 91.5 degrees) over the entire range of co mposition. At all values of x, nickel cations preferentially occupies sites in an ordered-vacancy layer with only a small percentage (less t han or equal to 15%) residing at sites in a fully occupied metal layer . This distribution is close to that expected for the normal structure type. The absence of any significant dependence on x of the cation di stribution is reflected in the magnetic properties, which show relativ ely little compositional variation. Electronic properties, however, in dicate a change in the nature of the valence electrons with decreasing nickel content.